There is known a flange type pipe joint used to connect pressure piping. The flange type pipe joint includes a welding type flange and a loose flange, etc. For example, Patent Document 1 discloses the welding type flange, wherein a flange is welded on an end portion of each of two pipes, a sealing member is interposed between the flanges of the pipes, and then each of the flanges is tightened by bolts. This flange is so called a plate flange, being an example of plug welding wherein the top face and the inside of the inside diameter of the flange are respectively welded. Further, Patent Document 1 indicates a loose flange type pipe joint wherein a loose flange is fitted on the pipe, and then, an end portion of the pipe is flange-machined on the pipe end portion, and the pipes are butted through a sheet packing on both surfaces of the flanges, and the flanges are tightened with the bolts. The loose flange is used to connect low pressure pipes. A butt welding-type flange, a socket welding-type flange, a screwed-type flange, etc. are known other than a flange disclosed in Patent Document 1. In the screwed-type flange, welding is not needed.
Patent Document 5 discloses an example wherein the flange is fixed on the pipe with screws. In this example, the pipe is inserted into the central part of the flange, the screws are screwed from the side of the flange toward the pipe, and the pipe is fixed on the flange. In this example, the tip of the screw is formed into an acute angle, and bites into the pipe when the screw is inserted. A technology disclosed in Patent Document 5 is related to pipes used in a vacuum airtight condition, wherein the pipes are pressed each other under atmospheric pressure.
As a method to connect pipes by adhesive or bolts without using flanges, for example, Patent Documents 2 and 3 respectively disclose methods to insert the pipes from both ends of a cylindrical joint and connect them. In these cases, the pipes are to house electric wires, and the bolts are screwed on the periphery wall surfaces of the pipes along the radial direction, and the pipes are deformed by tightening force of the bolts to be fixed. Thus bolted pipes are to protect the inside electric wires, namely unlike a fluid, the wires in themselves have no pressure, and there is no fear of liquid leakage. Patent Document 4 discloses a technology for connecting bars by bolts, wherein the bar sides are deformed by tightening force of the bolts to be fixed like Patent Documents 2 and 3.
Patent document 6 discloses a cylindrical sleeve covering across the pipes. The sleeve is provided with through holes in which bolts are inserted toward the pipes. One of the pipes has a fitting groove for catching the tips of the bolts with no clearance therebetween. It is possible to apply appropriate pressure on a seal by fitting the bolts into the fitting groove in a state that the pipes are pressed each other arranging the seal between their end faces.
Connecting pressure pipes for leading high-pressure fluid needs to secure a sealing performance for inner fluid. A sealing member for closing tight clearance between the pipes can exhibit the sealing performance by being loaded in a compression state. However, the sealing member must be exchanged when it is secularly changed by pressure, temperature and erosion of the inner fluid not to keep the original sealing performance. According to the connecting method using flanges, the sealing member can be easily exchanged by removing the bolts fastening the flanges. The above-mentioned conventional cylindrical joint is not related to the pressure piping. However, if using the cylindrical joint for the pressure piping, the cylindrical joint itself must be removed from the pipes, and therefore, workloads are increased.